Fatal crash caused by wing failure, NTSB says

Corrosion was the culprit in the wreck that killed 4 men last year.

Wing failure caused a floatplane crash that killed four men in the Katmai National Park and Preserve last year, according to a federal accident report.

For months, the crash puzzled investigators.

Though there were clues that the plane had suffered a structural failure -- its rapid descent caused ground scars -- there were no obvious signs that a wing had broken off.

When it crashed, the Helio Courier was carrying two Canadian businessmen, a Homer fishing guide and a Wasilla pilot who had just ended a day of fly-fishing at a remote lake. The floatplane hurtled into trees and tundra about 10 miles from its destination, the Royal Wolf Lodge, killing them all.

The co-owner of the lodge, Chris Branham, discovered the wreckage after an aerial search that afternoon.

"That kind of accident never leaves you," Branham said in a satellite phone call from the lodge on Friday.

He said he flies over the crash site nearly every day of the summer and still doesn't understand what went wrong.

The victims: Wasilla pilot Bruce Stephens, Homer fishing guide Tom Beatty, and brothers Greg and Sean Brophy of Ontario. Greg Brophy was the founder and chief executive of an international information security firm, Securit.

Investigators found the wings next to the wreckage. Usually, a failed wing would be found much farther away, said Clint Johnson, a National Transportation Safety Board investigator.

But after the wings were taken apart, laboratory tests showed corrosion in a spot where a wing attaches to the plane. The corrosion weakened the connection. Fractures on a massive bolt -- about 1 inch in diameter -- showed the stress was emanating from the corroded area, according to the NTSB report.

ALERT

As a result of those findings, the Federal Aviation Administration sent a special bulletin on Sept. 9 to all Helio operators, asking them to look for corrosion in the fittings for the plane's forward wings.

The corrosion might be hard to spot.

Someone would have to take the wings off the plane -- an intensive and complicated process -- in order to see the amount of corrosion discovered during the NTSB investigation, Johnson said.

"That is one of the things to wrestle with: how to inspect without taking the wings off," he said.

But if there's corrosion on the outside of the fittings, there's probably corrosion on the inside, he said.

It's hard to say for sure when corrosion became a problem on this plane, he said.

A BEEFY PLANE

Branham said he bought the plane from legendary Bush pilot Lowell Thomas in the 1980s, and his lodge uses three other Helio Couriers.

The reason his company chose this type of plane for the lodge was its reputation as one of the safest in the world, he said.

It's hard to accept that a plane of that caliber would have a structural failure, he said: It's so strong.

"All the pilots I've talked to have said, 'Gee, that must have been an isolated incident.' "

But this was not the first time the Helio Courier has had a problem with wing separation. In the 1980s, federal officials required owners of Helio planes to install new fittings where the wing attaches to the fuselage, Branham said.

Also, this particular plane was flying on salvaged wings.

In 2000, the plane lost power and had a hard landing near Port Alsworth. The salvage dealer told the NTSB the replacement wings were undamaged before they were sold to the Branhams, according to the report.

After last year's fatal crash, Branham removed the wings from the three remaining Helio planes used at the lodge for a thorough inspection.

He said he noticed a small amount of corrosion on the replacement fittings where the wing attaches to the fuselage and he thinks it's because they were improperly machined in the 1980s. But he said the corrosion appeared to be minor.

He's not sure what to make of the NTSB's findings.

"I think they've done their very best," he said. "But to me, there are still questions."

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Fonte: Flight Safety Information 23/09/2008.